The feasibility of monitoring regional and global vegetation using visible and near-infrared reflectance observations by AVHRR on board NOAA satellites has been demonstrated. The difference of vertically and horizontally polarized brightness temperatures ( DELTA T) at 37 GHz frequency (wavelength about 8 mm) of the scanning multichannel microwave radiometer (SMMR) on board the Nimbus-7 satellite has been processed as monthly composites of global observations from January 1979 to December 1985. The major factor determining the magnitude of DELTA T are scattering and absorption of microwave radiation by the vegetation, but one could also see the effects of surface roughness, open water (lakes and rivers) and snow cover on the observations. The DELTA T data have been found to be highly correlated with the normalized difference vegetation index derived from AVHRR, rainfall and drought over the Sahel, seasonal variation of atmospheric CO//2 concentration at Mauna Loa, land surface evaporation and primary productivity over hot arid and semi-arid regions of Africa and Australia.
